1. Field of the Invention
This invention relates to fluid flow control valves and more particularly to those valves for use in industrial systems requiring control of high pressure chemical and other fluids.
2. Background
There has long been a continuing use in the chemical industry and others for fluid control valves which are adapted for high pressure fluids, and that can be adjusted to accurately set flow to any percent of maximum flow rate at a fixed inlet pressure. Such fluid control valves are characterized as employing an axial plunger or stem and a manually rotatable knob to adjust the position of the plunger in the valve body. Setting the flow rate is effected by rotating the cap or knob to a marked position that corresponds to a given percentage of the maximum rated flow.
Several available fluid control valves have the capability of setting and roughly adjusting a flow rate to within a few percent, which has satisfied the process needs of many users in the past. However, a substantial number of present day users now require a finer flow control, allowing valve flow rate to be set at levels including a fraction of 1 percent. For example, at one part of a given mixing process, the required flow rate could be 15.7% with an accuracy of better than within +/xe2x88x920.5% of rated maximum flow. This is difficult to obtain accurately with presently available rough flow control valves, although some valves have marked adjustments corresponding to 0.5% or less of flow rate. In industry practice, any valve having a flow adjustment capability of 1.0% steps, would be calibrated and flow rate set at the desired level prior to installing the valve in the system, to achieve the required process flow rate. This practice precludes any possibility of adjusting the flow rate after a valve is installed. There is therefore a need for a flow control valve that includes provision for micro or fine adjustment of fluid flow after the valve has been installed. The fine adjustment would be in 0.1% steps over a small range, in addition to the currently available rougher adjustment steps. For many research and development applications, a valve adjustment accuracy of better than within +/xe2x88x920.3% of maximum flow rate is required. Therefore, an improvement in adjustment accuracy to better than within +/xe2x88x920.3% of maximum flow rate is also needed.
A principal object of this invention is to provide a micro or fine adjustment means for controlling fluid flow, that comprises a combination of mechanical components which interact with the structure of a high pressure flow control valve to produce changes in the valve stem position and thereby in valve fluid flow, in steps of 0.1% of maximum valve flow rate. A secondary object is to increase the present accuracy of valve flow control settings to better than +/xe2x88x920.3%. Further objects and advantages of the invention will be apparent from studying the following portion of the specification, the claims and the attached drawings.